1. Field of the Invention
The present invention relates to a vibration type driving apparatus. In particular, the invention relates to a vibrator that generates vibrations obtained by combining two different vibration modes with each other and a vibration type driving apparatus having the vibrator.
2. Description of the Related Art
A vibrator using a piezoelectric element that functions as an electro-mechanical energy conversion element is used for an oscillator, an actuator, or the like. In the above-mentioned vibrator, a resonance frequency is decided on the basis of a material characteristic, a shape, and dimensions, but because of a characteristic fluctuation in a piezoelectric material forming the piezoelectric element or a working error of part dimensions, a fluctuation in the resonance frequencies of the individual vibrators is caused. Since the resonance frequency of the vibrator directly affects an output characteristic of the vibrator, an adjustment on the resonance frequency needs to be conducted.
In particular, in a case where the vibrator and a driven member are relatively moved by vibrations obtained by combining two different vibration modes (vibration shapes) with each other, a resonance frequency difference between these two vibration modes needs to be contained in a desired relationship.
As a method of adjusting the resonance frequency, the following methods are proposed. One is a method of adjusting the resonance frequency by changing the dimensions of the vibrator. For this method, a method of removing a part of the vibrator through a laser process to decrease the dimensions is disclosed (see Japanese Patent Laid-Open No. 6-204778). The other one is a method of utilizing an electro-mechanical conversion effect of the piezoelectric element. According to this method, a driving electrode and an adjusting electrode are provided on a surface of the piezoelectric element provided to the vibrator, and the resonance frequency is adjusted through insulation and continuity of the driving electrode and the adjusting electrode (see U.S. Pat. No. 7,671,518).
However, like Japanese Patent Laid-Open No. 6-204778, according to the method of removing a part of the vibrator to change the dimensions of the vibrator, since heat is applied at the time of the process and a change in the material characteristic occurs, which may lead to a degradation in a vibrating characteristic. Also, a readjustment may be difficult because of the noninvertible process of removing the part of the vibrator.
Also, according to the method disclosed in U.S. Pat. No. 7,671,518, since the process is applied on the vibrator for the adjustment, a readjustment may be difficult once the adjustment has been conducted, and in a case where the adjustment is to be implemented, the procedure is complex. Furthermore, an output of the vibrator changes since the size of the driving electrode is changed along with the adjustment processing, which may cause a fluctuation in the output.